The invention relates to a method for the production of molten metal. Oxygen, a reducing agent and iron reduced in a reduction reactor are introduced into a melt gasifier. The reducing agent is gasified with the oxygen. The reduced iron is melted by means of the heat which occurs in this case. The cupola gas from the melt gasifier is used as at least a fraction of the reduction gas. Reacted top gas is drawn off from the reduction reactor. The invention also relates to a plant for carrying out the method, including one or more reduction reactors having a reduction gas supply, a melt gasifier having an oxygen supply, and a supply system for reducing agent, at least one line for the supply of the cupola gas from the melt gasifier into the reduction reactor and at least one line for drawing off the top gas from the reduction reactor.
In melt reduction plants, as described, for example, in DE 36 28 102 A1, oxygen with a temperature of 25° C. and a purity of ≧95% by volume is injected into the melt gasifier via the nozzles in order to gasify the reducing agents (predominantly coal and coal briquets) and make the required heat available for melting the reduced iron. The cupola gas from the melt gasifier (ESV) is used for indirect reduction in a fixed-bed reduction shaft (FBRS) or in fluidized-bed reactors (WSR), and is thereafter drawn off as top gas. The purified export gas, which is composed of the blast furnace gas from the direct reduction assembly and of the cupola gas from the melt gasifier, has the following typical analysis at 1.5 barg: CO 45% by volume, CO2 30% by volume, H2 19% by volume, H2O 3% by volume and N2 3% by volume. It has to be delivered for utilization and overall energy optimization on account of the gas excess.
However, not only the top gas or export gas from melt reduction plants contains large sensible heat quantities (top gas temperatures lie around 250° C.-500° C.), but also the fraction of the reduction gas which is not introduced into the reduction reactor, but is used as excess gas for the pressure regulation of the plant and as cooling gas. The temperature of the reduction gas lies around 700° C.-900° C. To utilize export gas in a power station (steam power station or gas and steam power station) or for metallurgic utilization (for example, direct reduction plant), the gas has to be purified of the impurities (dust, tar) contained in it. For this purpose, nowadays, wet scrubbers are mostly used, which at the same time cool the gas to about 40-45° C. and thereby extract the predominant fraction of the sensible heat from the gas. The heat is dissipated by the process water and discharged into the surroundings by a cooling tower.